Recording and reproducing medium and a recording and reproducing apparatus

ABSTRACT

A recording and reproducing medium includes: at least one recording and reproducing layer; and a heating layer which receives light for writing data, converts a part of energy of the light into heat, and selectively heats a desired portion of the recording and reproducing layer, thereby changing optical characteristics of the desired portion, wherein the heating layer converts the part of energy of the light into the heat by a surface plasmon resonance phenomenon.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording and reproducing medium andto an apparatus for recording and reproducing data in the medium byusing a laser beam.

2. Description of the Related Art

In general, optical disks (e.g., a compact disk) have been widely usedfor reproducing data in music or moving picture fields, because of thelarge capacity and low price thereof. The optical disks have also beenused for peripheral equipment such as a computer, etc. In this field, itis required that the optical disks record and reproduce data. Theoptical disks generally use a thermal recording method. In this method,a laser beam for recording and reproducing data, emitted from a lightsource such as a laser device is condensed at a minute spot of arecording and reproducing medium. The optical characteristics of theminute spot region of the recording and reproducing medium are changedwhen being heated, whereby data is recorded therein. In such a thermalrecording method, since the efficiency at which the energy of the laserbeam is converted into heat is not high, high-speed recording andreproducing are difficult to perform, requiring the light source for alaser beam with a high output.

In recent years, in order to overcome the above-mentioned problem, areproducing method using a surface plasmon resonance phenomenon isproposed in Japanese Laid-Open Patent Publication No. 4-14620. In thismethod, a recording layer can be made thin, so that data is recordedusing a light source for a laser beam with a relatively low output.

Hereinafter, a conventional example of a recording and reproducingsystem aiming at high-speed recording will be described with referenceto FIG. 9.

A medium 4 is filled between a prism 103 and a metal layer 101. Themedium 4 has a refractive index ns which is smaller than the refractiveindex np of the prism 103 and has a thickness of d1. In general, themedium 4 should satisfy np>ns. The medium 4 is usually air (in thiscase, ns is about 1). As an incident light 106, a P-polarized lighthaving a wavelength of λ is incident upon the prism 103 at an incidentangle θ larger than a critical angle θc. When the incident light 106 isincident upon the prism 103 at a particular angle θ1, an evanescent wavegenerated under an interface (i.e., the bottom face of the prism 103) isresonated with the vibration of plasma present between the medium 4 andthe metal layer 101, thereby causing the surface plasmon resonancephenomenon. Because of this, the reflectance of the incident light 106is reduced. In general, it is desired that the thickness d1 is smallerthan a wavelength λ of the incident light 106.

FIG. 10 is a graph showing the relationship between the reflectance ofthe incident light 106 and the incident angle θ thereof, where θ is avariable. A solid line shows the change in reflectance of the incidentlight 106 with respect to the incident angle θ. As is understood fromFIG. 10, the angle of the incident light 106 at which the surfaceplasmon resonance phenomenon is caused is θ1. When a dielectric thinfilm 102 having a thickness of d2 smaller than d1 is formed on the metallayer 101, the angle of the incident light 106 at which the surfaceplasmon resonance phenomenon is caused is θ2, and in this case, thecharacteristic curve of the reflectance is represented by a broken linein FIG. 10. In this way, the characteristic curve of the reflectancewith respect to the incident angle θ in a portion where the dielectricthin film 102 is formed is different from that in a portion where thedielectric thin film 102 is not formed. If the surface of a recordingand reproducing medium is scanned under the condition that the incidentangle θ is fixed at θ1, the amount of reflected light in a portion wherethe dielectric thin film 102 is formed is different from that in aportion where the dielectric thin film 102 is not formed, whereby areproduced signal A can be obtained.

On the other hand, during the recording, a laser beam is directlyirradiated to the dielectric thin film 102 and the dielectric thin film102 is melted or sublimed with the heat generated at a beam spot to forma pit therein. The dielectric thin film 102 can be formed of en organicmonomolecular film or a layered structure including 8 plurality offilms.

However, in the above-mentioned structure, recording data is performedby melting or subliming selected portions of the dielectric thin film102, so that recording new data cannot be repeatedly performed. Inaddition, separate light sources are required, respectively forrecording and reproducing. Moreover, it is difficult to improve therecording density, because the recording density is determined by thespot size of a laser beam.

SUMMARY OF THE INVENTION

The recording and reproducing medium of the present invention, includes:

at least one recording and reproducing layer; and

a heating layer which receives light for writing data, converts a partof energy of the light into heat, and selectively heats a desiredportion of the recording and reproducing layer, thereby changing opticalcharacteristics of the desired portion,

wherein the heating layer converts a part of energy of the light intoheat by a surface plasmon resonance phenomenon.

In one embodiment of the present invention, the recording andreproducing layer is made of a phase-transition type material.

In another embodiment of the present invention, the recording andreproducing layer is made of a magneto-optic material.

In still another embodiment of the present invention, the heating layeris made of metal.

In still another embodiment of the present invention, theabove-mentioned medium further includes a substrate supporting therecording and reproducing layer and the heating layer.

In still another embodiment of the present invention, the heating layeris separated into a plurality of portions.

In still another embodiment of the present invention, the plurality ofportions of the heating layer are arranged in a stripe shape.

In still another embodiment of the present invention, theabove-mentioned medium further includes a substrate supporting therecording and reproducing layer and the heating layer, the substratehaving a surface on which a plurality of grooves are formed,

wherein the plurality of portions of the heating layer are provided inthe plurality of grooves.

In still another embodiment of the present invention, each width of theplurality of stripe-shaped portions is smaller than a spot diameter ofthe light.

In still another embodiment of the present invention, a distance betweenthe respective plurality of stripe-shaped portions is smaller than thespot diameter of the light.

In still another embodiment of the present invention, the plurality ofstripe-shaped portions are arranged at a predetermined pitch in aregular manner, and the pitch is smaller than the spot diameter of thelight.

In still another embodiment of the present invention, the plurality ofportions are arranged in a matrix.

In still another embodiment of the present invention, theabove-mentioned medium further includes a substrate supporting therecording and reproducing layer and the heating layer, the substratehaving a surface on which a plurality of grooves are formed,

wherein the heating layer is formed on the surface of the substrate.

In still another embodiment of the present invention, an upper surfaceof the heating layer includes at least a first surface region at a firstlevel and a second surface region at a second level which is higher thanthe first level.

In still another embodiment of the present invention, the upper surfaceof the heating layer includes a third surface region at a third levelwhich is between the first level and the second level.

In still another embodiment of the present invention, the first surfaceregion and the second surface region are alternately arranged in a firstdirection, and the first surface region and the third surface region arealternately arranged in a second direction perpendicular to the firstdirection.

In still another embodiment of the present invention, the first surfaceregion and the second surface region are alternately arranged in a firstdirection, and the second surface region and the third surface regionare alternately arranged in a second direction perpendicular to thefirst direction.

In still another embodiment of the present invention, a width of atleast one of the first surface region and the second surface region issmaller than a spot diameter of the light.

In still another embodiment of the present invention, the first surfaceregion and the second surface region are arranged at a certain pitch ina regular manner, and the pitch is smaller than the spot diameter of thelight.

In still another embodiment of the present invention, a differencebetween the first level and the second level is not more than awavelength of the light.

According to another aspect of the present invention, an apparatus forrecording and reproducing data in a recording and reproducing medium isprovided, the medium including:

at least one recording and reproducing layer; and

a heating layer which receives light for writing data, converts a partof energy of the light into heat, and selectively heats a desiredportion of the recording and reproducing layer, thereby changing opticalcharacteristics of the desired portion,

wherein the device includes: a recording light irradiation unit forirradiating the light to the heating layer under the condition that asurface plasmon resonance phenomenon is caused on the heating layer; and

a reproducing light irradiation unit for irradiating light for detectinga change of optical characteristics of the desired portion to therecording and reproducing layer.

In one embodiment of the present invention, the recording lightirradiation unit irradiates an evanescent light to the heating layer asa recording light.

In another embodiment of the present invention, the reproducing lightirradiation unit irradiates an evanescent light to the recording andreproducing layer as a reproducing light.

In still another embodiment of the present invention, the reproducinglight irradiation unit detects the change of the optical characteristicsof the desired portion by using the surface plasmon resonance phenomenoncaused by the evanescent light.

In still another embodiment of the present invention, the reproducinglight irradiation means includes a detector for detecting the change ofthe optical characteristics of the desired portion, the detectordetecting P-polarized component and S-polarized component of thereproducing light.

Thus, the invention described herein makes possible the advantages of(1) providing a recording and reproducing medium capable of repeatedlyrecording and reproducing data, and recording end reproducing datasmaller than the spot size of a laser beam, and (2) providing arecording and reproducing apparatus using the same.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a recording and reproducing medium according to the presentinvention.

FIG. 2A shows an example of the recording and reproducing mediumaccording to the present invention.

FIG. 2B shows another example of the recording and reproducing mediumaccording to the present invention.

FIG. 3A shows still another example of the recording and reproducingmedium according to the present invention.

FIG. 3B shows still another example of the recording and reproducingmedium according to the present invention.

FIGS. 3C and 3D are partial cross-section views taken along lines A-A'and B-B', respectively, of FIG. 3B according to the invention.

FIG. 4 shows still another example of the recording and reproducingmedium according to the present invention.

FIG. 5 schematically shows a recording and reproducing apparatus whichrecords and reproduces data in the medium according to the presentinvention.

FIG. 6 is a graph showing the relationship between the reflectance ofincident light and the incident angle thereof in the recording andreproducing medium according to the present invention.

FIG. 7 shows the principle of recording in an example of the recordingand reproducing medium according to the present invention.

FIG. 8 shows the principle of recording in another example of therecording and reproducing medium according to the present invention.

FIG. 9 shows the principle of a recording and reproducing apparatuswhich records and reproduces data in the conventional recording andreproducing medium.

FIG. 10 is a graph showing the relationship between the reflectance ofincident light and the incident angle thereof in the conventionalrecording and reproducing medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described by way ofillustrative examples with reference to the drawings.

FIG. 1 shows a recording and reproducing medium 7 in a card shapeaccording to the present invention. The reference numerals 1, 3, and 5denote a substrate, a heating layer, and a recording and reproducinglayer, respectively. On the substrate 1, the heating layer 3 (thickness:100 nm) made of a metal film such as Au is provided. On the heatinglayer 3, the recording and reproducing layer 5 (thickness: 40 nm) isprovided. The recording and reproducing layer 5 can be made of ephase-transition type material whose refractive index is differentdepending on states such as a crystalline state and an amorphous state.Alternatively, the recording and reproducing layer 5 can be made of amaterial having a magneto-optic effect.

FIG. 1 shows the recording and reproducing medium 7 on one side of whichrecording and reproducing are performed. However, the recording andreproducing medium 7 can be made so that recording and reproducing areperformed on both sides thereof. In addition, the recording andreproducing medium 7 can be in a disk shape instead of a card shape.

FIG. 2a shows an example of the recording and reproducing medium 7 ofthe present invention. The heating layers (thickness: 100 nm) 3 areprovided so as to fill grooves (depth: 400 nm, width: 500 nm) 9 formedon the substrate 1. The recording and reproducing layer (thickness: 40nm) 5 is provided so as to cover the substrate 1 and the heating layers3. It is desired that the depth of the grooves 9 is equal to or lessthan a wavelength (typically 100 to 400 nm) of incident light used forrecording and reproducing data.

FIG. 2B shows another example of the recording and reproducing medium 7of the present invention. In this example, a plurality of recessedportions 10 are formed in a matrix on the substrate 1. For example, thesize of each recessed portion 10 is 500 nm×500 nm. Because of thisstructure, the recording position of each data can be restricted to eachrecessed portion 10. Thus, it becomes easy to discriminate data when thedata is recorded and reproduced; as a result, the data can be recordedand reproduced with good reliability.

FIG. 3A shows another example of the recording and reproducing medium 7of the present invention. In the same way as in FIG. 2A, the grooves 9are formed on the substrate 1. The heating layer 3 is made of a metallayer and formed by a sputtering method, etc. It is desired that thethickness of the heating layer 3 is set so that second groove 11 isformed in each of the grooves 9.

In this example, after the continuous heating layer 3 is formed over thegrooved substrate 1, the recording and reproducing layer 5 is formed onthe heating layer 3. The upper surface of the heating layer 3 has firstsurface regions 14 (concave regions) and second surface regions 16(convex regions). The data can be selectively recorded on the firstsurface regions 14 or on the second surface regions 16.

FIG. 3B shows another example of the recording and reproducing medium 7of the present invention. In this example, each first surface region 14has mounted portions 12 as preformat pits. The level of the mountedportion 12 is higher than the first surface region 14 and lower than thesecond surface region 16. In this example, erasable data is repeatedlyrecorded and reproduced on the first surface regions 14 or on the secondsurface regions 16, based on the change in characteristics of therecording and reproducing layer 5. The erasure of data such as tracknumber, signal position detecting data, etc. will damage the operationof the apparatus. In this example, such data is pre-recorded byarranging the position of the mounted portions 12. The data based on themounted portions 12 will not be erased, improving the reliability of theoperation of the apparatus. In FIG. 3B, each mounted portion 12 isprovided on each first surface region 14. Alternatively, a concaveportion can be provided on each second surface region 16 instead offorming the mounted portion 12 on each first surface region 14. Inaddition, each mounted portion 12 can be provided in a zigzag manner,instead of in a straight manner as shown in FIG. 3B.

FIG. 4 shows another example of the recording and reproducing medium 7of the present invention. The substrate 1 is flat and the heating layer3 is formed thereon. The grooves 9 are formed in the heating layer 3 bya semiconductor fabrication technique (e.g., lithography and etchingtechnique), and the recording and reproducing layer 5 is formed thereon.

FIG. 5 shows the principle of a recording and reproducing apparatuswhich records and reproduces data in the recording and reproducingmediums as shown in FIGS. 1, 2A, 2B, 3A, 3B, and 4.

The medium 4 and the recording and reproducing layer 5 are filledbetween the prism 13 and the heating layer 3. The medium 4 has arefractive index ns smaller than a refractive index np of the prism 13,and the total thickness of the medium 4 and the recording andreproducing layer 5 is d1. Here, the recording and reproducing layer 5is made of a phase-transition type material having a thickness of d2(smaller than d1) and a refractive index nt.

In general, the medium 4 and the recording and reproducing layer 5should satisfy np>ns and nt>ns, respectively. The medium 4 is generallyair (in this case, ns is about 1). As an incident light 15, aP-polarized light having a wavelength of λ is incident upon the prism 13at an angle θ larger than a critical angle θc. The reference numeral 20denotes a lens for condensing the incident light 15 at a bottom face 18of the prism 13. When the incident light 15 having a particular incidentangle θ1 is incident upon the prism 13, an evanescent wave generatedunder the interface (i.e., the bottom face 18) ks resonated with thevibration of plasma present between the recording and reproducing layer5 and the heating layer 3 to cause a surface plasmon resonancephenomenon. Because of this, the reflectance of the incident light 15 isreduced. In the case where ns, np, and nt are determined, mainparameters for causing the surface plasmon resonance phenomenon at thehighest efficiency are the angle θ of the incident light 15, thewavelength length λ thereof, and the thickness d1.

FIG. 6 is a graph showing the relationship between the reflectance ofthe incident light 15 and the incident angle θ thereof, where θ is avariable. In general, it is desired that the thickness d1 is smallerthan the wavelength λ of the incident light 15. The refractive index ntof the recording and reproducing layer 5 made of a phase-transition typematerial is locally different depending on portions thereof. That is tosay, the refractive index nt in a portion 19 where data is to berecorded is different from that in a portion 17 where data is not to berecorded. In FIG. 6, the change of the reflectance of the incident light15 with respect to the incident angle θ in the portion 17 is representedby a solid line and the change of the reflectance in the portion 19 isrepresented by a broken line. As is understood from FIG. 6, in theportion 17, the angle of the incident light 15 at which the surfaceplasmon resonance phenomenon is caused is θ1. In the portion 19, theangle of the incident light 15 at which the surface plasmon resonancephenomenon is caused is θ2. In this way, the reflectance of the incidentlight 15 with respect to the incident angle θ in the portion 19 isdifferent from that in the portion 17. When the surface of the recordingand reproducing medium is scanned under the condition that the incidentangle θ is set at θ1, the amount of reflected light is varied dependingupon the portions of the recording and reproducing layer 5, whereby areproduced signal a can be detected.

In the case where data is recorded in the above-mentioned recording andreproducing medium, the surface plasmon resonance phenomenon is alsoused. When the surface plasmon resonance phenomenon is caused, thereflectance of the incident light 15 becomes close to 0. Because ofthis, as shown in FIG. 7, the optical wave is coupled with the vibrationof plasma generated on the surface of the heating layer 3, and part ofthe optical wave is converted into heat in the heating layer 3. Therecording and reproducing layer 5 is heated by the heat generated in theheating layer 3, whereby thermal recording 15 performed.

Thus, the recording of data is performed by setting the incident angleθ1 so that the surface plasmon resonance phenomenon is caused at theportion 17 and by setting the amount of the incident light 15 so thatthe temperature of the recording and reproducing layer 5 is sufficientlyraised by the heat generated in the heating layer 3.

The data recorded in the recording and reproducing layer 5 is erased byanother optical system having the structure similar to that describedabove. If the incident angle of the incident light 15 is θ2, the datacan be erased in the same process as that during the recording.

In addition, a higher recording density can be obtained as follows: Asshown in FIGS. 3A, 3B, and 4, unevenness is provided on the surface ofthe heating layer 3, the surface plasmon resonance phenomenon is causedonly at concave regions or only at convex regions of the heating layer3. Alternatively, as shown in FIGS. 2A and 2B, the surface plasmonresonance phenomenon is selectively caused at portions where the heatinglayers 3 are filled. The surface plasmon resonance phenomenon issensitive to the incident angle θ of the incident light 15 and to thethickness d1. Thus, as shown in FIG. 8, in the case where the convexregions are formed so that the thickness between the bottom surface ofthe prism 13 end each top surface of the convex regions is d1, thesurface plasmon resonance phenomenon is generated only at the convexregions to heat the heating layer 3, but heat is not generated in theconcave regions. On the other hand, in the case where the concaveregions are formed so that the thickness between the bottom surface ofthe prism 13 and each bottom surface of the concave regions is d1, thesurface plesmon resonance phenomenon is generated only at the concaveregions to heat the heating layer 3, but heat is not generated in theconvex regions.

Due to the above-mentioned characteristics, the following is possible:

For example, when a width T of each concave region or each convex regionis set to be equal to or less than a beam spot diameter φD, only theconvex regions or only the concave regions are selectively heated.Therefore, data which is smaller than the beam spot diameter can berecorded and reproduced.

In the case where the recording end reproducing layer 5 is made of amagneto-optic material, the principle of the recording is the same. Thatis, the heating layer 3 is heated due to the surface plasmon resonancephenomenon, whereby thermal recording is performed in the recording andreproducing layer 5. In the case where the recording and reproducinglayer 5 is made of a magneto-optic material, when the temperature of therecording end reproducing layer 5 exceeds a Curie temperature, themagnetic field in an adequate direction is applied, in response to thecontents of data, to the recording and reproducing layer 5, whereby datais recorded. In this case, the refractive index of the recording andreproducing layer 5 is hardly changed by recording data. Thus, theamount of change in the intensity of the reproducing light as reflectedis remarkably decreased. However, the reproduced signal can be obtainedby detecting the change of an S-polarized component and a P-polarizedcomponent of the reflected light. This detection can be performed by adetection optical system of a conventional magneto-optic recordingapparatus.

In this recording and reproducing medium, the recorded data can beerased by the same optical system as that used for recording. However, abias magnetic circuit for inverting the direction of the magnetizationof recorded data is required.

In the examples of the present invention, the thickness of the heatinglayer 3 can be several μm, as long as the thickness is sufficientlylarger than the depth of penetration of incident light for recording andreproducing data. The heating layer 3 can be made of a metal materialwhich efficiently causes a surface plasmon resonance phenomenon andwhich is thermally stable. Examples of the metal material include Au,Pt, etc. The thickness of the recording and reproducing layer 5 isdesirably 1000 Å or less. In addition, the thickness d1 shown in FIG. 5is preferably equal to or less than a wavelength of the incident light15. It is more preferred that the thickness d1 is as small as possible.For example, assuming that the incident light 15 is an He-Ne laser beam,the wavelength thereof is about 0.63 μm. In this case, it is preferredthat the thickness d1 is 0.1 μm or less.

As described above, according to the present invention, because of thesurface plasmon resonance phenomenon, light energy can be efficientlyconverted into heat energy. The efficiency can be set at 90% or moreunder ideal conditions. This shows that according to the presentinvention, an efficiency twice that of the conventional system can beobtained. Moreover, because of the unevenness of the surface of therecording and reproducing medium and the pattern formation on theheating layer, the local surface plasmon resonance phenomenon can beselectively caused. Thus, data is recorded and reproduced at awavelength or less of the incident light.

Various other modifications will be apparent to and can he readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A recording and reproducing medium comprising:atleast one recording and reproducing layer; and a heating layer whichreceives light for writing data, converts a part of energy of the lightinto heat, and selectively heats a desired portion of the recording andreproducing layer, thereby changing optical characteristics of thedesired portion, wherein the heating layer is a metal material which isseparated into a plurality of portions, as part of a generally planarsurface, for converting the part of energy of the light into the heat bya surface plasmon resonance phenomenon to change the opticalcharacteristics of the desired portion of the recording and reproducinglayer, and the heating layer has a thickness which is larger than thedepth of penetration of incident light for recording and reproducingdata.
 2. A recording and reproducing medium according to claim 1,wherein the recording and reproducing layer is made of aphase-transition material.
 3. A recording and reproducing mediumaccording to claim 1, wherein the recording and reproducing layer ismade of a magneto-optic material.
 4. A recording and reproducing mediumaccording to claim 1, wherein the metal material is Au or Pt.
 5. Arecording and reproducing medium according to claim 1, furthercomprising a substrate supporting recording and reproducing layer andthe heating layer.
 6. A recording and reproducing medium according toclaim 1, wherein each portion of the plurality of portions of theheating layer is a stripe shape.
 7. A recording and reproducing mediumaccording to claim 6, further comprising a substrate supporting therecording and reproducing layer and the heating layer, the substratehaving a surface on which a plurality of grooves are formed,wherein theplurality of portions of the heating layer are provided in the pluralityof grooves.
 8. A recording and reproducing medium according to claim 6,wherein the light has a predefined Spot diameter and each width of theplurality of stripe-shaped portions is smaller than the spot diameter ofthe light.
 9. A recording and reproducing medium according to claim 6,wherein the light has a predefined spot diameter and a distance betweenthe respective plurality of stripe-shaped portions is smaller than thespot diameter of the light.
 10. A recording and reproducing mediumaccording to claim 6, wherein the light has a predefined spot diameter,the plurality of stripe-shaped portions are arranged at a predeterminedpitch in a regular manner, and the pitch is smaller than the spotdiameter of the light.
 11. A recording and reproducing medium accordingto claim 1, wherein the plurality of portions are arranged in a matrix.12. A recording and reproducing medium according to claim 1, furthercomprising a substrate supporting the recording and reproducing layerand the heating layer, the substrate having a surface on which aplurality of grooves are formed,wherein the heating layer is formed onthe surface of the substrate.
 13. A recording and reproducing mediumaccording to claim 1, wherein the recording and reproducing layer is acontinuous layer.
 14. A recording and reproducing medium comprising:atleast one recording and reproducing layer; and a heating layer forreceiving light for writing data, converting a part of energy of thelight into heat, and selectively heating a desired portion of therecording and reproducing layer thereby changing optical characteristicsof the desired portion, wherein the heating layer is a metal materialfor converting the part of energy into heat by a surface plasmonresonance phenomenon and wherein an upper surface of the heating layerincludes at least a first surface region at a first level, a secondsurface region at a second level which is higher than the first level,and a third surface region at a third level which is between the firstlevel and the second level, the surface regions at the first, second,and third levels occupying respective substantially parallel planes. 15.A recording and reproducing medium according to claim 14, wherein thefirst surface region and the second surface region are alternatelyarranged in first direction, and the first surface region and the thirdsurface region are alternately arranged in second directionperpendicular to the first direction.
 16. A recording and reproducingmedium according to claim 14, wherein the first surface region and thesecond surface region are alternately arranged in a first direction, andthe second surface region and the third surface region are alternatelyarranged in a second direction perpendicular to the first direction. 17.A recording and reproducing medium according to claim 14, wherein thelight has a predefined spot diameter, and a width of at least one of thefirst surface region and the second surface region is smaller than thespot diameter of the light.
 18. A recording and reproducing mediumaccording to claim 17, wherein the light has a predefined spot diameter,the first surface region and the second surface region are arranged at acertain pitch in a regular manner, and the pitch is smaller than thespot diameter of the light.
 19. A recording and reproducing mediumaccording to claim 14, wherein the light has a predefined wavelength anda difference between the first level and the second level is not morethan the wavelength of the light.
 20. A recording and reproducing mediumaccording to claim 14, wherein the recording and reproducing layer is acontinuous layer.
 21. A recording and reproducing medium according toclaim 14, wherein the metal material is Au or Pt.
 22. A recording andreproducing medium according to claim 14, wherein the heating layer hasa thickness which is larger than the depth of penetration of incidentlight for recording and reproducing data.
 23. A recording andreproducing medium according to claim 14, wherein the heating layer is acontinuous layer.